The purpose of this contract is to characterize the in vivo chemical toxicity in laboratory animals associated with short term exposures generally ranging from two to thirteen weeks. The studies performed under this contract will identify possible target organ(s) toxicity, similarities and differences in sensitivity between sexes and species of animals and dose response relationships. The data from these studies will also be used by the National Toxicology Program for establishment of dose levels of chemicals selected for subsequent long-term carcinogenicity studies.